Golf club head

1. A hollow iron-type golf club head comprising: a heel portion, a sole portion, a toe portion, a top-line portion, a front portion, a rear portion, and a striking face having an unsupported face area of between about 300 mm2 to about 4,000 mm2; a back wall in the rear portion enclosing a substantial portion of the rear portion to create a substantially enclosed cavity, the enclosed cavity being defined by at least a rear surface of the striking face, an inner back wall surface, and the sole portion; at least one plug located within the enclosed cavity, the at least one plug being compressed between the rear surface of the striking face and the back wall in the rear portion; wherein the unsupported face area includes a thickened central region; and wherein the at least one plug is positioned to be in contact with at least a portion of the thickened central region; wherein the back wall includes at least a first aperture, the first aperture being configured to allow the at least one plug to be inserted into the first aperture and is configured to allow the at least one plug to move from a first position to a second position; and wherein the back wall includes at least one slot, the at least one slot being connected to the first aperture and is configured to secure the at least one plug.

2. The iron-type golf club head of claim 1 , wherein the enclosed cavity has a volume between about 1 cc and 200 cc.

3. The iron-type golf club head of claim 1 , wherein the at least one plug contacts the inner back wall surface.

4. The iron-type golf club head of claim 1 , wherein the striking face includes a welded striking plate.

5. The iron-type golf club head of claim 1 , wherein a total striking face area is between about 2,700 mm 2 and about 5,000 mm 2 .

6. The iron-type golf club head of claim 1 , further comprising a filler material located within the enclosed cavity, the filler material substantially surrounding the at least one plug and being configured to hold the at least one plug in place.

7. The iron-type golf club head of claim 6 , further comprising an aperture into the enclosed cavity, the aperture being configured to allow the cavity to be filled with the filler material.

8. The iron-type golf club head of claim 7 , wherein the filler material is an expanding foam material having a density between about 0.03 g/cc and about 0.19 g/cc.

9. The iron-type golf club head of claim 6 , wherein the filler material occupies about 50% to about 99% of the total club head cavity volume in the enclosed cavity.

10. The iron-type golf club head of claim 6 , wherein the filler material completely fills a remaining cavity volume around the at least one plug.

11. The iron-type golf club head of claim 6 , wherein the filler material contacts an entire first side surface of the at least one plug.

12. The iron-type golf club head of claim 1 , wherein the at least one plug weighs about 0.5 g to about 1 g.

13. The iron-type golf club head of claim 1 , wherein the at least one plug weighs about 0.7 g or less.

14. The iron-type golf club head of claim 1 , wherein the at least one plug has a hardness of about 10 to about 70 Shore A hardness.

15. The iron-type golf club head of claim 6 , wherein the filler material and the at least one plug have a combined weight of less than about 20% of the total club head weight.

16. The iron-type golf club head of claim 6 , wherein the filler material and the at least one plug have a combined weight of less than about 5% of the total club head weight.

17. The iron-type golf club head of claim 1 , wherein the back wall includes a first aperture.

18. The iron-type golf club head of claim 1 , wherein the back wall includes a first aperture having at least a first diameter and a slot configured to match at least a keying portion of the at least one plug.

19. The iron-type golf club head of claim 1 , wherein the coefficient of restitution of the club is greater than about 0.8.

20. The iron-type golf club head of claim 1 , wherein the striking face includes a striking plate formed of a steel selected from the group consisting of maraging steels, maraging stainless steels, and PH stainless steels.

21. A hollow iron-type golf club head comprising: a heel portion, a sole portion, a toe portion, a top-line portion, a front portion, a rear portion, and a striking face having an unsupported face area of between about 300 mm2 to about 4,000 mm2; a back wall in the rear portion enclosing a substantial portion of the rear portion to create a substantially enclosed cavity, the enclosed cavity being defined by at least a rear surface of the striking face, an inner back wall surface, and the sole portion; at least one plug located within the enclosed cavity, the at least one plug being compressed between the rear surface of the striking face and the back wall in the rear portion; wherein the back wall includes a first aperture; wherein the first aperture is configured to allow the at least one plug to be inserted into the first aperture and is configured to allow the at least one plug to move from a first position to a second position and wherein the back wall includes at least one slot, the at least one slot being connected to the first aperture and is configured to secure the at least one plug.

22. The iron-type golf club head of claim 21 , wherein the first aperture has at least a first diameter and a slot configured to match at least a keying portion of the at least one plug.

23. The iron-type golf club head of claim 21 , wherein the at least one plug weighs about 0.5 g to about 1 g.

24. The iron-type golf club head of claim 21 , wherein the at least one plug weighs about 0.7 g or less.

25. The iron-type golf club head of claim 21 , wherein the at least one plug has a hardness of about 10 to about 70 Shore A hardness.

26. The iron-type golf club head of claim 21 , wherein the coefficient of restitution of the club is greater than about 0.8.